In gas chromatography (GC) systems, the amount of time required for a chemical compound to traverse the entire length of a separation column (“column”) is known as its retention time. One factor that contributes to the retention time of a chemical compound is the temperature of the separation column. Controlling the temperature of the column precisely from analysis to analysis is beneficial to provide repeatability in the retention time for a particular chemical compound or analyte. In addition, programmatically changing the column temperature while the sample components are migrating through it can advantageously provide shorter analysis time and reduce peak broadening.
Often, columns are heated in known systems using an air convection oven because of its ability to provide a uniform and repeatable thermal environment in a space large enough to accommodate a wide variety of column diameters and lengths. The columns are typically arranged on a support structure such as a basket that creates an open cylinder of column coils, with open space inside and outside the cylinder. This allows the heated air access over all the column surfaces and results in uniform temperatures across the entire column length. While air convection ovens are useful, their use comes with clear disadvantages. For example, convection ovens require a significant amount of energy and time to heat up, and a significant amount of time to cool down. This leads, of course, to comparatively long cycle times and high power consumption, among other disadvantages. In addition, the ability to do rapid analysis via temperature programmed conditions is limited when using air convection ovens.
Conduction or “resistive” based technologies have been actively researched for the promise of faster heating and cooling rates but adoption has been slow because design tradeoffs have often forced the technology to be optimized for only certain niche markets. Low Thermal Mass (LTM) column modules are available in which the fused silica capillary column is bundled together with a heater element and temperature sensor. The result of bundling the heater, sensor and column together is the most direct transfer of heat, resulting in programming rates as fast as approximately 1800° C./min using under 200 W of power. However, the analytical results are not as repeatable as when an air bath oven is used. Also, the disadvantage of bundling the column with its heater and sensor is that a customer must replace the heater and sensor with the column (e.g., when the column is fouled or broken, the heater must also be replaced). In addition, bundled columns are liable to have reduced lifetime due to their construction and the concentration of stresses on the column tubing.
What is needed, therefore, is an apparatus that overcomes at least the drawbacks of known GC column heaters.